1. Field of the Invention
The present invention relates to a defect detecting method of detecting defects in crystals or an amorphous material such as an amorphous semiconductor and optical glass, and also to a defect detecting device used in the method.
2. Description of the Related Art
When a laser beam gathered by a condenser lens is incident into the crystal, defects in crystals are detected by an image formed from scattered light and emitted light caused by defects in the crystals of a specimen. The scattered light and emitted light are gathered and focused by an optical system. The light signals transmitted from the specimen include various kinds of light having various wavelengths and intensities, such as elastic scattered light, inelastic scattered light, and photoluminescence light, which are caused in interactions between the entering laser beam and impurities and defects in the host crystals.
Conventional crystal defect detecting methods include a method of detecting defects by observing the total intensity of all the light signals transmitted from the specimen, a method of detecting defects by observing Raman scattering light, and a method of detecting defects by observing photoluminescence light. In these conventional methods, since there is only one specific characteristic light for each inherently physical phenomenon, observation of defects in the crystals has been implemented by taking out such characteristic light respectively.
For instance, the light scattering tomography method is used as an essential way of evaluating and controlling quality of silicon wafers, because of its high performance in detecting defects, such as dislocation, deposition, point defects, plane defects, and segregation impurities, in transparent crystals.
By the light scattering tomography method, however, defects smaller than several tens nm in diameter are difficult to detect due to noise, and high density defects which is beyond the resolving power of the detecting optical system are undetectable. Also, types of defect cannot be identified by this method.
There is another method called Raman scattering tomography method in which a Raman spectroscope is incorporated into a detecting device by the light scattering tomography. By this Raman scattering tomography method, information on the chemical composition of crystal defects can be obtained. However, the signal-to-noise ratio is poor due to the low intensities of the light signals obtained. As a result, it is difficult to distinguish defects from the light signals from the base.
With a method using photoluminescence light, there are problems that detectable defects are limited, and that positional resolving power is low.
As can be seen from the above description, by a single method, light signals generated by factors other than the factor that causes the light signals to be detected result in noise and lower the signal-to-noise ratio. Moreover, using only one method is disadvantageous in that no detailed information on the interrelationship between elastic scattered light, inelastic scattered light, and photoluminescence light can be obtained.